Sulphonated polymers have been known for some time. Non-crosslinked sulphonated vinyl polymers have been known since at least the early nineteen sixties.
U.S. Pat. No. 3,072,618 issued Jan. 8, 1963 in the name of Albin F. Turback, assigned to Esso Research and Engineering, discloses a process for the sulphonation of non-crosslinked polystyrene. In fact the disclosure of the patent makes it clear that it is important to reduce the number of crosslinks to the smallest possible number (Col. 1, line 31). The object of U.S. Pat. No. 3,072,618 was to prepare water soluble polymers which would be useful as thickeners, impregnants, adhesives, soil conditioners and textile sizes.
Greek Patent 86.0636 in the names of G. Valkanas and P. Rigas issued Mar. 18, 1986 discloses that polystyrene crosslinked by reaction with a di-alkylhalo aromatic compound in the presence of a Lewis Acid is useful in agricultural applications after it has been sulphonated. The Greek Patent discloses a process for sulphonation in which a gel of the crosslinked polystyrene is sulphonated with sulfuric acid. From a practical point of view such a process results in a significant amount of acid water which must be separated and treated before safe disposal. This is a disadvantage which needs to be overcome before the technology disclosed in the Greek Patent can be effectively commercialized.
The polymers disclosed in the Greek Patent are not water soluble as they are intended to stay in the ground to hold water in the soil. The polymers disclosed in U.S. Pat. No. 3,072,618 are intended to be water soluble. Interestingly applicants have discovered that the process designed for use with non-crosslinked polymers is also useful with crosslinked starting materials in accordance with the present invention.
U.S. Pat. No. 4,209,592 issued Jun. 24, 1980, assigned to Rohm and Haas Company discloses a process to manufacture ion exchange resin. In the process SO.sub.3 is used both as a crosslinking agent and as a sulphonating agent. Uncrosslinked polystyrene is reacted directly with SO.sub.3 in an halogenated solvent. While the resulting polymer is a sulphonated crosslinked vinyl aromatic monomer it does not have the same water uptake as the polymers of the present invention. Particularly, the sulphonated croslinked vinyl aromatic polymers of the present should have a water up take of at least 15000, preferably 20000, most preferably 25000 or greater weight % of water. It is clear from the examples of U.S. Patent the water uptake is below about 100 weight %.
U.S. Pat. No. 4,448,935 issued May 15, 1984, assigned to National Starch and Chemical discloses a process for simultaneously crosslinking and sulphonating polystyrene. The patent contains a limitation that the process is conducted a low temperatures from 0.degree. to 25.degree. C. The process of the present invention operates a higher temperatures than those disclosed in the reference. The process of the present invention provides a controlled sulphonation process which may be carried out at elevated temperatures. Most importantly the process does not introduce a significant further amount of crosslinking into the crosslinked polymer.